Key heads for typewriters, calculating machines and the like



June 30, 1959 R. HEINZE ET AI. 2,892,529

KEY HEADS FOR TYPEWR-ITERS, CALCULATING MACHINES AND THE LIKE Filed March 24, 1954 INVENTORS. RICHARD HEINZE.

KURT ALTMANN.

ATTORNEY United States KEY HEADS FOR TYPEWRITERS, CALCULATING MACHINES AND THE LIKE This invention is concerned with improvements in or relating to the construction of key heads for a key-board operated machine, e.g. typewriters, calculating machines and similar office machines. Key-heads for these machines are known which consist of cast, moulded or pressed-cores carrying letters, figures, or other characters andwhich have cast or pressed aroundthem a jacket or casing.

According to the present invention there is provided a key-head for a key-board operated machine such as a typewriter or calculating machine comprising a core of tough material moulded to shape so as to include a character or symbol and means for securing it to a key-lever,

, and a casing of hard material moulded around said core with the character exposed at a surface of the casing.

Preferably the tough material which is moulded or die cast is cellulose acetate while the harder material of the casing is preferably a'polyacrylic acid ester.

With the construction of the invention the hard and smooth die-cast material which constitutes the surface proper of the key-head is not exposed to or is only slightly exposed to mechanical stresses. Further characteristic features and advantages of the key-heads of the invention will be apparent from the following description.

Several embodiments of the invention will now be de scribed with'reference to the drawings, wherein:

Figure l is a'vi'ew from'below of one form of core acrcording to the invention,

7 Figure 2 is a cross section'through the core of Figure 1,

Figure 3 isa 'plan'view'of this core,

Figure 4 is a cross section through a completed keyhead,'the section beingtaken at right angles to that shown Figure'Z, l

Figure 5 is a plan view of the key-head in Figure 4,

Figure 6 is a section through a modified key-head,

Figure 7 is a further cross section of the key-head shown in Figure 6 but at right angles thereto,

Figure 8 is a view from beneath of a still further modified key-head, and

Figure 9 is a cross section through the key-head of Figure 8.

In Figures 1 to 5 reference numerals 1 indicates the body of a core made from a soft tough die-casting material, which has an internal trough-shaped hollow space 2 of rectangular cross section for the reception of a key-lever shaft, not illustrated. The top of the hollow space is formed by lattice-like bars 3 between which are apertures 4. The bars make possible in the manufacture of core 1, in a known manner, the influx of casting material to all parts of a symbol or character 5 while on the other hand the apertures 4, during the embedding or casing of the core with a differently coloured mass, make possible the influx of the casting material to the enclosed inner spaces or less accessible or isolated parts of a symbol or character. The core is provided with a nose or projection 6 which extends up the top half of the core. The smaller walls of the core have dome-like recesses 7 through which latter, in the casting of the casing, there is formed a bridge of hard casting material. The outer periphery of the core is circular and is suitably provided with a rim or flange '8. In Figure 2 the jacket or casing is indicated by dotted lines 9.

A section through the core 1 coated with a hard casing 9 is shown in Figure 4, while Figure 5 shows a plan view of the completed key-head. An annular space 10 is left free between the core and the casing, so that the resilient rim 11 of the hard casing is relieved of mechanical stresses. The trough-shaped hollow space is made larger than would be necessary for the reception of the keylever shaft and the residual interspace at the long sides of the rectangular hollow space 2 is filled with hard material 12 so that when pressing in the key-lever, indicated by 13, contact is permitted substantially only between the key-lever 13 and the hard coating 12 (preferably flank-like but solidly adhering). This construction has the advantage, that the harder steel material of the key-lever is guided better into the hard artificial 'cast material than into the soft artificial cast material. A fracturing of the hard material 12 is prevented by the softer surrounding core 1. There is thus obtained properties similar to those given by the use of case hardened steel for machine parts. Furthermore, by the attachment of the hard layer to the long sides of the slot or hollow space in the core, the influx of hard material to the less accessible parts of the enclosed letters or characters is facilitated during the casting of the hard material casing. The recesses 7 are likewise filled with hard material and neighbouring radial fillets 14 and 15 are formed of hard material, so that all parts which consist of hard material are united to one another and there is obtained, at the same time, a strong union and interlocking between the core 1 and the casing 9. The fillet 14 at the same time surrounds the nose 6.

As can be seen from Figure 5 the core and the inner wall of the casing 9 are circular in shape, while the outside of the casing is approximately heart-shaped.

The union between the artificial materials of the core and key base and the casing which'are of different hardnesses should be so shaped that the parts fit tightly on one another and cannot be separated from one another in the use of excessive strength. However the soft artificial material should be able to undergo elastic deformation without stresses resulting in the surr'oundinghard artificial material. The deformation of the core or base in a" keyhead can be very considerable indeed if the key-lever shank has large deviations from the true shape, which deviations may appear in its breadth through the tolerances of the sheet and in its length through inaccuracies of the cutting tool. The present faults in materials also make it necessary to work with less accurately turned or rolled strips or sheets. For this reason the embodiment shown in Figures 1 to 5 does not always suflice.

In order in such cases, to avoid, if possible, over-stressing of the materials the core can be, as illustrated in Figures 6 and 7 made from two parts separately manufactured, the base of the key-head being made from soft material, and the symbol or character carrying part being made from hard or soft material, both the parts being held clamped together by the casing consisting of hard material.

In this construction the part 21, as in the first example, is provided with a letter or numeral 22 which projects into the surface of the casing 23 and is visible therethrough. The character or symbol carrying part 21 is fitted to the key base 24 consisting of a soft tough material which again has in its centre a longitudinal slot 25 for pressing onto the key lever, not shown. The part 21 is provided on its underside with pins, which can engage loosely in holes or sockets 26 in the flange 27 extending from the top of the key base 24, so that both parts can be joined together outside 3 the casting mould. After insertion in the mould casting with the hard mass of the casing 23 takes place, the key base for the most part being .left freely spaced from the hard-casing, so that the material can, in this event, yield during the pressing on ,of

the key-lever. However, the part 21 and the flange 27 .the casing being unduly highly stressed. The variations in the shape are for the most part taken up by the soft material.

A still greater adaptation to any fluctuations in the material stress of the key-lever can be obtained if the keyhead is provided, at the periphery of the slot in the keybase, with additional recesses which are not filled by the key-lever and make possible a yielding of the tough artificial material through the abnormalities of the key-lever shaft. Through yielding of the material displaced by the key-lever into the lateral recesses the pressure on the wall of the key-head can be maintained within permissible limits and the formation of cracks can be avoided. An embodiment for this purpose is shown in Figures 8 and 9. In this embodiment 31 indicates the key-head casing consisting of hard material which casing is pressed around a symbol or character carrier 32 of a different colour so that the already mentioned intimate mutual anchoring exists. The key-head 31 provided with a rounded-off square key-surface is pressed well around the key-base 33, which consists of a somewhat softer yieldable material, for example Ultramid." The securing slot 34 in the key-base 33 is widened at its periphery by a series of additional recesses 35. If the key-lever of rectangular cross section is inserted in the slot 34 it lies tightly in the fundamental rectangular shape of the slot 34, so that the material displaced by the key base 33 can expand into recesses 35. With this construction the deficiencies arising during pressing on due to relatively large tolerance excesses are practically annulled in a favourable manner.

The character carrier 32 can in this case also consist of hard or medium-hard material since it is manufactured separately from the key-base 33, as in the example shown in Figures 6 and 7, and any stresses set up during pressing are equalized.

Experiments have shown that with the use of a suitable material, as for example Ultramid, variations of shape by, for example, 0.3 mm. of the base of the keyhead can still be well taken up without cracks resulting. The flexibility of the base of the key-head, due to the mentioned construction of the slot, makes it possible even to use a key-head with one and the same slot size for key-levers with different shank measurements. For example, a key-head which is made for a shank measurement of 6 x 1 mm. is also used for a key-lever with a shank measurement of 6 x 1.2 mm., whereby still sufficient play remains for the tolerance of the sheet.

We claim:

1. A key-head for a key-board operated machine comprising a two-part core having a character-carrying part and a base part of soft tough material the two parts being separately moulded to shape, means in the base part for securing it to a key-lever and a casing of hard material moulded around said core to hold the two parts of the core together in clamp-like manner with the character exposed at a surface of the casing.

. 2. A key-head in accordance with claim 1 wherein the two parts of the core are joined together by co-acting pins and sockets prior to the application of the casing.

3. A key-head for a key-board operated machine comprising a two part core having a character-carrying part and a base part, the latter being of soft tough material, the two parts being separately moulded to shape; means in the base part for securing it to a key-lever; and a casing of hard material moulded around said core but spaced from the main side parts thereof to hold the two parts of the core only at the upper ends together in clamp-like manner with the character exposed at a surface of the casing.

4. A key-head in accordance with claim 3 wherein said two parts of the core are joined together by co-acting pins and sockets prior to the application of the casing.

5. A key-head in accordance with claim 3 further including an apertured flange on the upper surface of the base part and pins on the lower surface of the charactercarrying part registering with the apertures in the flange.

6. A key-head in accordance with claim 5 wherein the soft material of the bast part is cellulose acetate and the hard material of the casing and other parts is a polyacrylic acid ester.

References Cited in the file of this patent UNITED STATES PATENTS Switzerland Mar. .952, 

